


Submerged.

by Raynefall, Werepirechick



Category: Teenage Mutant Ninja Turtles (TV 2012), Teenage Mutant Ninja Turtles - All Media Types
Genre: Action/Adventure, Alternate Universe - Canon Divergence, Apocalypse, Boats and Ships, Developing Friendships, Diving, Gen, Hijinks & Shenanigans, Hunters & Hunting, Lots of that, Male-Female Friendship, Ocean, Ocean Apocalypse AU, Other Additional Tags to Be Added, Post-Apocalypse, Scuba Diving, Swimming, Underwater, Water, also lots of that, culture clash, just day-to-day life in the aftermath of a world scale event, lots of fun things to do out there, not too much!, scavenging, this is mostly just a happy post-apoc AU
Language: English
Status: In-Progress
Published: 2017-08-30
Updated: 2018-10-08
Packaged: 2018-12-21 16:22:45
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence
Chapters: 7
Words: 6,667
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/11948037
Author URL: https://archiveofourown.org/users/Raynefall/pseuds/Raynefall, https://archiveofourown.org/users/Werepirechick/pseuds/Werepirechick
Summary: In their efforts to terraform the earth, the Kraang cause a world-scale climate change and subsequent flooding. Most of the earth is now ocean, entire coastal cities swallowed by the sea as it rose; temperatures soaring to tropical levels nearly everywhere, and aquatic creatures becoming dominate over formerly land-bound ones.Life perseveres though, and with it, the lives of those who survived the flooding.(Ocean Apocalypse AU)





	1. Prelude: exposition on the AU's contents.

**Author's Note:**

> hey folks! i know i have a bazillion other stories on the go, but a friend of mine and i have started an on-going AU over on tumblr. i had to share the results so far, and hopefully bring another few people on board with the idea. :D
> 
> [here's the blog if you want to see the artwork and other things we have posted so far! ](https://submerged-tmnt.tumblr.com/) this fic and the blog will both be updated as content is created.
> 
> the blog itself is still a work in progress, but please bear with us and preemptively follow so you get all the good stuff first!
> 
> first chapter here is an exposition ripped directly from the temporary masterpost on the blog, written by my friend and co-author Rhi. the next chapter will be the very first drabble i've churned out for the series. exposition on the series will change as we edit and update the facts, so mind it whenever you check in on this fic; you might learn something new!

About a week or so after the turtles first got mutated, the Kraang screwed up while trying to test their terraforming, and accidentally flooded Earth. For a while,t hey tested things to see if they could fix it, causing a flood of sea-adapted mutants, but eventually gave up and decided to leave for another planet. NYC is mostly underwater, with only a few buildings sticking up above. It looks something like this:

However, there a tons of boats, ziplines, docks, etc. connecting all of the buildings. It’s a big central hub for trading in whats left of civilized communities, with their main export being leftover artifacts from before the flood. Many people here are divers, and make a living trading off what they can scavenge from the depths. 

Because Splinter and the turtles were exposed to such a drastic change in their environment, the mutagen in the blood triggered to allow them to mutate somewhat further, giving them an advantage in the now flooded world. 

They live in the sewer system still, in one of the many pockets of air that remain down there, where the pressure is too great for humans to travel. Splinter rarely leaves the tunnels, instead, is practicing adapting ninjutsu to work underwater, and teaching his sons of what it was like before the flood.

> **The differences between the canon turtles and the Submerged turtles:**

  * Clawed and webbed hands and feet
  * Sharp teeth for eating food raw, since there’s nowhere to cook things. They mostly eat fish, though they also eat octopus, crabs, mussels, jellyfish (sometimes), anything they trade with April/Casey, and whatever else they can hunt.
  * Slightly different markings.
  * Different straps and weapons. No mask.
  * Due to the density of water, swinging weapons don’t work well. Instead, the boys have different weapons, mainly used for hunting, but also attacking the miscellaneous mutant or bandit. They all carry at least two small knives on them, and ink bombs.  
-Donnie has a fishing spear   
-Raph has serrated,[ barb-like](http://t.umblr.com/redirect?z=http%3A%2F%2Fwww.lafishblog.com%2Fwp-content%2Fuploads%2Fa-stingray-barb-1.jpg&t=MTI5ODk2MDIxOWUyZGU4NTdmMjg1ZmJmNzBlOTIwNDAwNzIwOWUyMCxyNUxTV3oxMA%3D%3D&b=t%3AY_gSWRU45njRLHByVRzG5g&p=https%3A%2F%2Fsubmerged-tmnt.tumblr.com%2Fpost%2F164739505544%2Fabout&m=1) daggers  
-Leo has short thrusting swords, not katanas  
-Mikey has a net, and usually more knives on him than his brother



 

  * Have their own, low-frequency language and mild echolocation. It only works when in the water, or if they’re touching on land. Generally only in their range of hearing.
  * Can hold their breath for approximately 3-5 hours when active, and days if they’re sleeping. 
  * Can drink saltwater. Like sea turtles, they cry to get rid of extra salt sometimes, not just when they’re sad.



* * *

  * **April**  is still a Kraang hybrid in this AU, but doesn’t learn it until much later. Due to this, she isn’t effected by the bends, and can dive just as deep as the turtles can. He hair is cut extremely short to reduce maintenance.
  * **Casey** is a normal human and is best friends with April, and later, the turtles. He’s a dork and just braids his hair instead of cutting it off. Some days he regrets this.
  * **The mutanimals** are still here, albeit somewhat changed. Leatherhead is a saltwater crocodile mutant, Dr. Rockwell is an octopus mutant, Pete is a seagull mutant, and Slash is a leatherback sea turtle mutant.
  * **Shredder** died at sea approximately 13 years after the flood. 
  * **Karai** inherited his empire and all of his possessions. She found a journal hidden in a locked safe that contained her true heritage, but never searched for Hamato Yoshi, believing him to be dead. However, when she got into a skirmish in NY, she spilled mutagen on herself, and was turned into a Belcher’s Sea Snake mutant. She eventually befriended the turtles and discovered her father was Splinter.
  * **Shinigami**  is Karai’s second in command and runs her empire while she’s away.  ~~Also her girlfriend.~~



* * *

> **Other random facts we’ll organize later**

  * Fruits, vegetables, and basically any food other than seafood is very hard to come by and very expensive.
  * The turts use their diving prowess to trade stuff with their humans in exchange for interesting foods and things they can’t salvage themselves.
  * Theres lots of skeletons at the bottom because of the sheer number of people that died in the first flood.
  * Mikey is a little hoarder, and has a room full of random things like shells, animal parts, odd trinkets that he can’t trade, jewelry, and human skulls. Whoops.
  * Donnie collects mutagen canisters leftover from when the Kraang were here, because Splinter isn’t stupid in this AU and actually told his sons the story of how he foUGHT ALIEN ROBOTS so that nobody else gets mutated
  * There’s lots of random sea mutants roaming the world, but not all are hostile. 
  * There’s lots of pirates/bandits roaming the seas, and the boys have a habit of sinking/raiding bandit ships (both for goods and the pleasure of taking down ‘bad guys’. Mostly for the goods).
  * _You bet your ass Karai is a kickass pirate snake empire leader._ Also, apparently Belcher’s Sea Snakes are like… 100x more venomous than rattlesnakes or something. Need to do a bit more research. Fun :)




	2. Sweet Winds

**Notes for the Chapter:**

> here's the first little bit! this was inspired by the discussion of what April and Casey's lives might be like, living in the post-apocalyptic world they do. short, but sweet like it's title.

April swims like she was born for it.

That’s what everyone says, at least.

She can’t remember a time she didn’t swim. Growing up in New York’s floating city, rather than the old world like her dad, means she’s a part of the generation that never knew anything else. The sea is temperamental and dangerous, filled with riptides and sudden squalls- but somehow, she’s never really feared it the same way most adults do.

Majority of her friends are similar, because the water is as much their normality as it is hers. But… at the same time, they don’t seem to have the same sense of _ease_ that she does. It’s been like that since she was old enough to go off on her own, swimming through the cool, salty waves with all the grace of the fish and aquatic mammals beneath the surface.

It feels right, like a second home to her. As equally comfortable as her creaky ship’s bunk.

And April’s never experienced diving sickness, not even once, even though she’s been diving as deep as she could nearly all her life. Bends happen commonly to careless divers, and April is… relatively careless, on occasions. She can’t help it; sometimes the currents just pull her into their flow, and she loses track of the rigid safety rules that’ve been instilled in them all. But even with that carelessness, she’s never risen too fast or dove too quickly. It’s like she just can’t.

Her friends are jealous, particularly Casey, a communal cook’s son, since he tends to be as careless as April.

And because of those things, the seafloor, further out to the edges of the city, where the old shore used to end- it sometimes seems like something she could _reach,_ if she just tried.

But, she’s restricted like everyone else, to the shallows. Easy to reach seafloors where everyone can dive to, if they’re good enough swimmers.

Her father worries, so April never strays _too_ far from those shallows.

But when a sea breeze blows just right, filling her lungs with salt and brine, she _has to go._

Usually speaking, Casey is up for a misadventure or two, and he goes with her. It’s one of the reasons he’s her best friend, seeing as any other of their peers would be too intimidated by the idea of being swept out to sea to venture beyond the shallows.

They take a skimmer those times, when the sun is bright and the winds are sweet, and sail to the far edges of the safe zone; into the deeper ranges of their sunken city. Where it’s dangerous to dive even _with_ an air tank.

April rarely dives with air tanks; her ability to hold her breath is legendary. Casey has to wear a tank, but not for lack of trying. To soothe his bruised ego, they typically split the difference and bring just one to share; majority going to Casey.

On those sweetly hot days, they tether their boat to an abandoned, flooded building, and dive deep as they dare. Passing swarms of fish, branches of coral, and descending past the dilapidated levels of the skyscrapers around them.

It’s because they’re so daring, and somewhat careless, that they eventually make a mistake and overstep their limits. Tunnels of stone only hold up so long, and pockets of air in them are dangerous to trust.

April thinks the terror of near death is worth it, later on. She figures Casey does, too.

After all, it led to them meeting the turtles, and both of them agree that anything would have been worth that.

**Notes for the Chapter:**

> honestly i love writing these two as straight up friends. they have excellent dynamic and chemistry, and are just a joy to see play off each other.
> 
> more coming soon as i write it, and drop by the blog to ask questions if you have any! you might inspire more drabbles if you do. :0c


	3. Pile Up

**Notes for the Chapter:**

> got inspired while i was reading an old favorite of mine, so thought i'd give a round of family fluff for ya'll.

A long day’s swim always tires them out, but a long day of actually  _interacting_  and  _talking_  and  _spending time_   _with people_ , besides just each other, is just plain draining.

They’re not exactly introverted- god only knew who would ever apply the term to  _Mikey_ \- but they’re certainly not adjusted to being around other people. It’s a thrilling and wonderful experience, but sometimes… too much, after a point.

It’s just different with family, and family time is needed right now to recover from having friend time.

Hence why after towels are thrown about, Mikey and Raph forced to remain still long enough to be somewhat cleaned of mud, and they’re done snacking on a few clams Mikey had tucked in his net-

They drag the miscellaneous and carefully hoarded pillows they’ve stolen or made over the years, all into one big pile to the side of their largest room and settle down into it as a group.

Mikey immediately dozes off, curled up and half buried into the pile and Leo’s side. He’d been running at nonstop full-throttle for nearly seven hours, and even though that’s usually nothing for him, doing it with Casey and April present seemed to take double the energy. Even hyperactive almost-extroverts need to recharge at the end of the day, it seemed.

He doesn’t regret it though, having to give a little more than he usually does to a situation. Friends are the  _best_   _thing_ , and it’s exhilarating to have someone to talk to besides his brothers. But, exhilaration takes it out of you, and even he’s not an exception.

Leo finds himself meandering before tucking in for a nap. In his hands he gently turns the pages of a rare and precious paperback novel; it’s one he never takes anywhere outside their home, at risk of ruining its delicately inked words. It’d been snatched from a foreign goods ship years ago, and while at the time he’d been scared shitless, he hasn’t stopped being grateful Donnie had grabbed it in the middle of the chaotic and ill-advise thievery attempt. 

While Mikey snoozes on his right, and Raph relaxes on his left, Leo loses himself in the concept of  _space travel_ , and the impossible idea of seeing other worlds. Friends are all well and good, especially since he’s only recently gotten them- but sometimes reading about someone else’s adventures is better than having his own.

Raph isn’t tired enough to sleep quite yet, but doesn’t feel like hunting down his sealed bag of sketching tools. He’s comfortable as he is, shoulder to shoulder with Leo and Donnie, and content to just think on what they did that day. Daylight swims near human settlements are new, and spending time with real humans just as; it’s fun, but exhausting, and he feels an unusual need to sit and digest what’s happened today. 

Casey introduced him properly to water polo, something they’d all only seen in passing. Raph and his brothers had all been challenged to a game of it by April and Casey, and somehow, despite being faster and stronger swimmers, they’d lost devastatingly. Raph figures some practice of the game was in order, soon as he stops feeling too tired to be assed to move. 

Donnie tinkers quietly, unwinding his thoughts and unconscious stressing of the day. He’s got a clock he salvaged recently, discovered after it was lost off someone’s house boat. He believes if he works at it long enough, he might be able to resurrect the waterlogged thing and return it to the humans who lost it.

April and Casey and been mostly encouraging about the endeavor, April sincerely and Casey somewhat mockingly. If anything though, the latter reaction has only made him want to try harder, if only to prove the human he  _can_  fix it. 

Even with the soft warmth of the pile, and the collective heat of the bodies in it, urging him to slow down and close his eyes- Donnie chooses to keep fiddling with the delicate clock parts and stave off his nap. Raph starts to drift off as he keeps working, and Donnie barely notices his brother laying his head on his shoulder. 

Their father drifts through the room a little later, tail and feet hardly making a sound as he does. By that point, only Donnie is still awake; Raph as asleep as Mikey, and Leo having laid his book on his plastron and shut his eyes. 

Splinter approaches his clustered sons, and gently takes the screwdriver out of Donnie’s hand. Donnie blinks, realizes how tired he is, and smiles sheepishly at his father.

Splinter puts a finger to his curling lips, giving a nod at Donnie’s peacefully slumbering siblings. A meaningful nod.

 _Go to sleep, my son,_  he says very clearly with just the gesture and his amused gaze. His sons having friends is something he is very happy about, but lately if they don’t have a chance to nap a bit, they’ve gotten temperamental and overtired even before dinner. Childish it may be for them, he thinks a nap before dinner and late evening fishing will be better than him having to break up squabbling.

Splinter gives Donnie a warm smile as his son releases his project and tools, settling down properly into the pile of fabric and musty smelling stuffing. With the clock and tools confiscated, he leaves Donnie to fully relax into the comfy communal sleep spot.

Leo has started snoring, whistling through his nose as he dozes; Mikey’s face is completely mashed into the pillows and Leo’s side, but somehow breathing fine. Raph is silent on Donnie’s shoulder, and breathing deep and even as he sleeps; Donnie’s eyes drift shut, his head full of new experiences and thoughts to sort through later, but put aside for the moment.

Their father puts Donnie’s tools and clock away in his room, carefully set on the cluttered desk inside, and by the time he returns, Donnie is completely asleep with all his siblings.

**Notes for the Chapter:**

> i love these boys, they're good and wonderful and i should write nice things for them more often.
> 
> next tho i wanna write stuff for my girl KARAI! (ft - being a giant fucking snake and unable to eat the little shits who did this to her)


	4. Copper Bright

**Notes for the Chapter:**

> i lied about the snake!karai thing, have some casey introspection instead.

The moment Casey hears their teacher say, _“O'Neil? O'Neil? Absent again, fantastic,”_ he knows why the seat next to him is empty.

He knew before then, too, but had been thinking it could’ve been just a late morning for April.

Of course it rarely was, but their teacher always seemed hopeful anyways

By the time lunch rolls around, Casey figures he’s had enough of school for the day. If he misses anything important, he could just bribe Irma for notes with some of those shrimp she likes so much from his dad’s restaurant.

“Skipping?” She asks mildly as they’re all let outside of the class. Sharp little eyes already knowing exactly where he’s off to.

“Got better places to be,” Casey replies equally as mild. He salutes he and keeps walking, headed for the staircase leading out of their school building. “Seeya, Langstein.”

“Lemme know if you two finally get it on together,” Irma calls after him, and Casey gives her a different sort of salute for that.

As he steps outside, into the busy centre of the New York, he knows why April didn’t even bother shooting him a heads up she’d be gone. The wind is enough to carry his loose shaggy air off his shoulders, warm and enticing. The sun is bright in clear skies and he can tell it’s a good day for diving.

Casey snags a snack on the way, paying a visit to a rare fruit vendor to get a stupidly expensive collection of apples. Worth it, but it hurts his wallet anyways.

The dockway shifts under his weight as he goes, leaving the bigger and more stable walkways behind as he heads outwards from the city. He ditches his sandals completely as he hits the houseboat district; walking on warm wood and metal that’s smooth from ocean waves.

He keeps walking, crunching on a green apple, and passes the homes by until they start to really get sparse. Then he keeps going, towards one of the least used docks. April’s favourite spot.

It’s still empty when he gets there, so Casey sits down with his netbag of fruit, and starts his lazy waiting for his best friend to get back.

He’s not mad April ran off without him. She’s always done this, and it’s just something he’s come to accept about her. When the sea calls- off goes O'Neil, faster than any fish or gull.

The heat is hardly kept off by the lapping ocean waves around his dangling legs, and Casey drops his shirt beside his shoes behind him. Shirts are overrated anyways.

Around two hours later, a familiar sail comes into view, and Casey grins.

April leans with the skimmer, shirt gone and tan, freckled skin on display. Her short hair sticks up every direction, and the sun makes it shine copper bright.

She catches sight of him, and the brilliant smile Casey is given makes his stomach pleasantly warm.

April guides the skimmer boat in, slowing it down and adjusting the sails with a lifetime’s expertise. Her shoulders and arms work to do so, and Casey follows the way her muscles tense as she commands her boat.

As she arrives at the dock, sun kissed and still dripping with salty droplets, Casey stares at his best friend and wonders if he could count every freckle on her body, if he was ever allowed that close.

“Nice tits,” He says, instead of saying _you’re the most beautiful person I’ve ever met._

April laughs, carefree and bright. “Nice tits yourself! Here, catch.”

She tosses her latest bag of treasures, dripping wet in a net, and hops lightly onto the dock. With quick efficiency, she starts roping the boat to the jutting poles.

Casey does not look at how nice her legs look while doing that, and examines the haul. He pulls out one thing with interest. “The hell is this thing? A weird skewer?”

“A pen, actually! An old fancy ink pen. Like, for calligraphy?”

“What?”

“Swirly writing, Jones.”

Casey wrinkles his nose. Right. “Why d'you need a pen for that? I thought you used paintbrushes.”

April stands up, pulling her shirt out of her diving belt and starting to unfortunately pull it over herself. Goodbye lovely O'Neil shoulders and abs. “On boats, yeah, but these were for paper and junk. Really popular back in the day, at some point.”

Casey looks at the weird pen in his hands, and thinks that sounds a little overly wasteful for their current world. Scribbling on carefully rationed paper with fancy ink and fancy ink pens- that’d all get wrecked in less than a drizzle. “Sounds stupid, if you ask me.”

“I didn’t, thank you, so fuck off,” April’s head reappears out of her t-shirt, making her short hair even messier. Cute. “I just thought they were neat and that maybe we could sell them to a trader ship. Land folks have plenty of paper far as I know, so I’m sure they’d like a fancy pen or two.”

Casey examines the thing for another moment, and then shrugs. “Sounds wasteful, but alright. They’re all weird anyways.”

April takes her treasures back from him, huffing fondly. “I’m sure they think the same about us. And some of those better be for me, mister.”

“Why should they be?” Casey asks, standing up and holding his apples near. “You abandoned me to schoolwork and went fancy pen hunting without me.”

“Give them here, jerk. I cut you in on my notes last class.”

“Nope.”

“Casey!” April laughs, and grabs for the bag.

Casey holds them above his head, and laughs in his short friend’s face as she hops for it. Eventually, because he is admittedly a little lenient with April, he lets her get it. Also because she’s awful and kicks like an evil little bitch.

Casey doesn’t think too hard about how close they’d been through that whole game of keep away, or how flushed and kissable April’s cheeks are after a day’s diving trip. Instead, he kicks her back, like their dynamic has gone since they were knee high, eats another apple, and gets into a rousing conversation of how lucky and weird inlanders are.

April suggests he comes with her to the latest of her discovered dive spots, and Casey agreed to the adventure like he always does.

(Things don’t go as they always do when they dive that time, he nearly lets slip some things he’d rather not quite yet, and their lives stop going “like always” from there on out. Mostly thanks to four very green and very inhuman teens with a tendency to attract more absurd events than any of them can keep track of.)

**Notes for the Chapter:**

> childhood friends scenario for casey and april results in privately very in love casey and oblivious april. i love it.
> 
> (he figured out he /liked her/ liked her when she punched a guy in the nose so hard it broke. it was all downhill from there.)
> 
> note about cultural norms in this AU: shirts are not a big priority, really, and tend to just get in the way of free diving. hence why april pretty much shamelessly walked around without a shirt for this whole thing, and casey hardly batted an eye. it's no big deal and actually just plain normal.


	5. Fishheads

**Notes for the Chapter:**

> i wrote the next two chapters ages ago on tumblr and forgot to add them here whoops

Casey watches, mouth hanging open, as his recently made friend bites the whole fucking head off a fish.

Raph swallows said head of fish, and gives Casey an annoyed look. “What? You never seen a guy eat fish before?”

Casey, as the son of a restaurant owner, tries to find words to express how wrong the whole situation is.

“You eat it  _raw??”_  Casey eventually exclaims, still horrified.

Raph tears off a strip of silver and red flesh, and drops it in his mouth. “Yeah, how else would you do it?” He asks, mouth full and giving Casey an  _are you stupid?_  kind of look.

“But-” Casey watches Raph tear another few strips off and feels sick. “-salmonella!”

“Salmon what now?” Raph asks. “This is cod, dumbass.” He eats another strip, and Casey, as, once again, the son of someone who prepares and sells food for a living, feels absolutely offended.

“It’s a  _disease!”_

 _“_ Cod? No, cod’s a fish. I’m literally eating it right now.”

“Not the cod!  _Salmonella!”_

 _“_ The fuck is that.”

Casey takes a deep breath, grabs Raph by his wet salty cheeks, and says right to his face, “ _The disease you get if you eat improperly prepared raw fish!”_

And Raph stares at him like  _he’s_  the one who’s crazy.

“Dude,” Raph says, absolutely unimpressed. “we’ve  _always_  eaten it raw. How do you eat raw fish wrong? You just eat it. How would you even screw that up?”

Casey releases Raph’s face, rocking backwards on the barely above the surface roof they’re on top of. He drags his hands down his face, unsure of how to explain food preparation laws and fallouts that humans have to deal with.

“Have you  _ever_  eaten it cooked?” Casey asks, because that would definitely be. Something.

Raph rolls his eyes. “We live in the ocean, and humans would see us if we went inland for wood to burn on a roof. How would have even?”

Casey thinks about that, still personally offended by Raph’s raw fish eating, and  _apparently_ also his entire family’s.

“Well,” He finally decided on. “we’re gonna have to fix that.”

Raph grunts, and eats another few bites of his freshly caught dinner. Casey tries to ignore the gut reflex of  _no no no bad do not eat fish raw like that_  and just eat his own snackish dinner; which is dried fish from a baggie he brought with him.

He succeeds until Raph bites off the head of  _another damn fish,_  and then Casey’s own fish tries to make a reappearance.

**Notes for the Chapter:**

> [based on a goofy doodle mod Rhi did a while back](https://submerged-tmnt.tumblr.com/post/164822015615/some-miscellaneous-doodles-i-did-today-to-get-a)


	6. Sharing Air

**Notes for the Chapter:**

> idk if people knew this or not but ot3 is the endgame here.
> 
> have some sappy jonatello.

Casey’s braid floats in the corner of his eye as he turns, caught in the current as he rolls to look up towards the surface. The sun shines through the shallows above him, illuminating the shadows swimming over him.

The brothers and April move without hindrance through the ocean waves, sweeping limbs carrying them sort of like how wings carry birds, except even more graceful. The ocean is quieter than the sky is, deep and nearly soundless. It swallows and cradles and gives and takes, and with the world how it is, it’s practically endless.

Casey loves it as much as anyone else in his city does, seeing as there’s no way to avoid it. His friends, though. They love it more than he could probably ever understand.

Maybe if he could swim like they did, for hours and hours without issue, like they were born in the swells of froth and salt, maybe he’d get it. He can’t though, so he’s stuck wearing the oxygen tank whenever they dive deep enough he’ll need it. And even though they’re diving shallowly today, he’ll need to go up for air again in just a few minutes. He’s not like them in a lot of ways, but he makes do; keeps up regardless.

Casey kind of wishes, sometimes, he could dive as deep and hold his breath as long as his friends. Though, the drawbacks of not being an aquatically inclined being sometimes also are benefits.

Like now, as Donnie catches Casey’s eye, and dives down to his level. Casey is months used to the turtle mutant drifting close underwater, putting his cool hands against Casey’s jaw and tugging him near. Fitting them together like two pieces.

Donnie’s lips are a lot cooler than April’s; reptilian smooth and only warm deeper in. Casey breathes out through his nose, and breathes in the air Donnie gives him through the kiss. Slow and long. He’ll bug Donnie later about having fish breath, but likely speaking, he’ll probably bug Casey about his own before then.

Donnie pulls away with a small smile, something warm in his deep red eyes as he looks at Casey. Casey was already comfortably warm in the summer waters, but that look warms him further, right to his core.

And then Mikey impacts against them, trailing bubbles as he laughs during a chase. Raph and Leo and April are all in hot pursuit of the smallest turtle’s escape, and the air Donnie just gave Casey escapes his lips as he startles into laughter.

As Casey begins to feel the need for air once again, giving a sheepish smile, Donnie rolls his eyes and takes him by the hand; ascending to the surface with swift strokes. Casey keeps hold of Donnie’s hand as they go.

**Notes for the Chapter:**

> will we update again sometime soon? god i hope so.


	7. Introductions

**Notes for the Chapter:**

> this au's co-author and my bestie rhi was having a bad night recently, so this au got resurrected at their request for more Submerged turtles.

Casey hefts the bucket of fish bones, balancing it on his hip so he can unlatch the door and push it open. The cool nighttime air gusts inside as he steps out, and Casey walks away from his home towards the other end of the dockway. The buoyant path linking all the surrounding houseboats rises and falls subtly under his bare feet, the ocean calm tonight.

Casey hums as he reaches the edge, holding the bucket out and tipping it to spill the bones into the dark water. Except something suddenly surfaces right where he’s aiming the bucket.

“ _Casey!”_ exclaims Leo, and Casey yanks the heavy bucket back just in time that he avoids dumping fish gunk on his friend. Unfortunately, the bucket is heavy and his luck isn’t having it tonight. His grip on the slimy plastic slips and fish bones spill onto the dockway.

“Uh oh,” says Mikey, joining Leo in poking his head out of the water. Donnie and Raph emerge as well, clear eyelids blinking away the saltwater in their eyes.

“Guys- c’mon!” Casey says, shaking a skeleton off his foot in disgust. “What the hell, I’m gonna have to clean that all up!”

“Sorry,” Leo apologizes sincerely, “but you were the closest person and we _really_ need help.”

Casey forgets the fish bones for a moment, coming back to the edge and kneeling down. “What’s up?” he asks, a bit worried despite his casual tone. Then he frowns, seeing the dockway lights shining on cuts and bruises the brothers have. “Hey, you guys look a little rough. Something happen?”

“We, uh… well,” Leo starts, looking sheepish. “It’s a bit complicated.”

The water underneath the dockway suddenly rises, making Casey wobble a little. “How so?” he asks, steadying himself with a hand.

“It’s not complicated,” Raph interjects before Leo can continue. He’s got a serious shiner and an annoyed scowl. “We got basically spent the whole day getting beat up by a snake.”

“Wh- a _snake?_ Like, a mutant one?”

“The fuck other kind of snake could do this to us?”

“Jesus,” Casey says. “That’s pretty kickass, I guess. If no one got hurt, right?”

“We’re fine,” Mikey assures him, giving a bright smile with a split lip. “Just sore and hungry.”

“Are you here for food? ‘cause we got some leftovers inside,” Casey says, jerking a thumb at his family’s restaurant houseboat behind him. The dockway rises and falls sharply again, which is getting kind of annoying and worrying. Maybe there’s a storm on the way? The clouds are wrong, though…

“Food would be good,” Mikey sighs longingly. “I’m starving.”

“Pen and paper is needed first, though,” Donnie says seriously.

“Uh, why?”

“Our friend needs it so she can tell us her name,” Leo explains, which doesn’t explain much at all.

Casey raises his eyebrows in interest anyway. “You guys make a new friend before or after the snake fight?” he asks, smile quirking his lips. The brothers could use more friends, seeing as they’re only willing to interact with Casey and April, and neither of them has managed to convince the four turtles to show themselves to the population of New York. Their phobia of people is a stubborn one.

“After!” Mikey cheers. He grabs Leo in a side hug, splashing Casey’s knees. “Leo sweet-talked her into it.”

“I didn’t s- sweet-talk her, jeez,” Leo says in a mumble. His brothers chuckle and elbow him, teasing their teal scaled sibling.

“So, where’s this lady of yours?” Casey asks gamely, grinning at Leo’s embarrassment. The dockway surges underneath him again, forcing Casey to steady himself with both hands and triggering a weird feeling in the back of his head. A shivery ‘something is wrong’ feeling.

“She came with us,” Donnie says, as the water around him and his brothers churns. And as he delivers that calm statement, something _big_ rises out of the water right behind them.

Casey gapes for a moment at the giant fucking snake his friends have brought to his doorstep. Then it opens its mouth and hisses viciously and Casey yelps, scrambling backwards from the edge of the dockway.

“Ah, it’s okay!” Mikey calls out. “We told her you’re our friend! That’s just how she talks. Kinda.”

The giant sea snake makes another hiss, followed by a sound that seems like it wants to be an actual word, but can’t fully form into one. Casey’s lifetime of being taught to fear a sea snake’s bite is rearing its head, causing sweat to bead his brow and his heart to race.

“You shitting me?” he asks, staring at the snake mutant. It- _she_ stares right back, luminous green eyes pining him with a gaze that’s got just an edge of feral. Kinda like the ones the brothers sometimes have.

“If only,” Raph grumbles, leaning on the dockway with his elbows. “This’d be a lot simpler if it were just a prank.”

“I second that,” Donnie says with a longsuffering sigh.

“Um, Casey? I know it’s a lot,” Leo speaks up, “but could you skip being shocked and just go get a pen and paper? We’d- well, _she’d_ like it if we could call her by her actual name, instead’ve just saying ‘you’ or ‘Miss Snake’.”

The snake mutant, though she still looks pissed off, bobs her head once in agreement. Casey runs a hand through his loose hair, feeling its long strands tangling after a hot and sweaty day.

“Uh, sure,” he says, shaking off his shock about the whole situation. “I’ll. Just go get those…”

The brothers are sitting on the dockway when Casey comes back, legs folded and scales glistening with seawater. Their usual weapons are present, but- Donnie’s spear has been broken at the tip, Raph is definitely down a couple knives, Mikey is missing his fishing net, and Leo seems to have lost one of his swords. Plus, with them out of the water, Casey can see the full extent of the injuries they garnered fighting with the snake mutant looming over them all.

Of course, the snake herself looks a tad banged up, too. Looks like the damage was all very mutual, until things got worked out.

“Okay,” Casey announces, sitting down next to his friends. “I hope you guys use my dad’s notebook wisely, ‘cause paper isn’t cheap.”

“We just need one page,” Leo assures him, taking the pad and pen. He turns his head, looking up at the serpent with jaws big enough she could swallow a small child whole. Leo smiles at said serpent. “Alright, like Donnie explained, I’m going to go through the alphabet letter by letter. Hiss, or, do whatever you want to whenever I hit a letter of your name in order. Ready?”

The snake mutant huffs impatiently.

“I figured,” Leo chuckles. He clears his throat, touching the pen to a blank page of the tiny notebook. “A, B, C, D …”

It goes on like that until Leo hits _K_ , and the snake mutant hisses loudly. Casey’s arms have goosebumps and his heart is skipping all over the place, and it’s kind of great. She’s _wickedly scary,_ teeth designed for piercing, a deadly bite to boot, and a long sinuous body that’s powerful enough to shake the dockway as she gets excited over the first letter of her name- god damn. There aren’t many mutants around this size or strength. Casey would _not_ (totally would) want to be the guy caught in the water with Miss Snake or whoever she is.

(He would probably die trying to take her on, but _fuck._ What a way to go, battling a giant seas serpent.)

“K?” Leo is saying excitedly. The snake mutant bobs her head _yes._ He writes the letter down hastily, and keeps on going with the alphabet for the next one.

Five letters later, and the snake shakes her head vehemently as Leo tries to start again. Leo looks confused for a moment, then lights up with a smile. “Oh! Is that it? Is this your name?”

The snake bobs her head.

Casey then ends up shoving slickly wet limbs out of the way so he can see the notebook, too. Leo gets squished by all four observers crowding in, little growling clicks coming from the back of his throat with his irritation.

“God, _guys,_ I was gonna read it out!” Leo snaps, elbowing everyone he can reach. Casey is shoved away, just like the rest of the brothers, but not before he sees what Leo has written in tight, painstakingly careful boxy letters.

_Karai_

“Karai,” Leo says aloud, still smiling at the snake leaning over them all. “That’s a really cool sounding name. It’s nice to meet you, Karai.”

“Hey, Karai!” Mikey tacks on, as Raph mutters a, “Hi, again,” and Donnie adds politely clipped, “Hello.”

“Sup,” Casey says, waving a hand. Karai regards them all with her wide green eyes, examining them for something, and then huffs.

She makes a softer hiss than any of the ones she’s made before, followed by something that’s nearly a word. Casey is pretty sure it’s supposed to be a _hello._ He grins.

So cool. Four quirky turtles who are weirdo recluses, and now a giant deadly sea snake. Casey’s friend group hasn’t ever been this colorful before, even with April and Irma as buddies.

“So, hey, Dee?” Casey asks, catching the attention of the least occupied brother, while the other three are focused on Karai. “How’d you all meet anyway?”

“Oh yeah, I don’t think we got a chance to tell you or April.” Donnie crosses his arm, letting out a resigned sigh. “We interrupted a deal between pirates, mostly on accident, since we were tracking a shipment of mutagen. It was _supposed_ to be an in and out operation, but _SOME PEOPLE-”_ he says loudly, shooting a look at Raph, “-can’t be damn well bothered to remember common manners!”

“We live in a tunnel system!” Raph protests snappishly. “How was I supposed to learn that shutting doors is what’s polite when we don’t _have fucking doors?”_

“It didn’t even matter if it was polite, you left the door _wide open_ , which was unusual for a tightly knit band of pirates who _always_ kept that door shut, which in turn alerted them to our presence and ruined the whole plan!”

“Shut up! Leo already bitched at me, you can’t, too!”

“So where’s Karai factor into all this?” Casey asks in a bemused voice, because Raph and Donnie are literally just hissing at each other now and that’s always hilarious. Donnie snaps something clicky and sharp and definitely turtle-speak for something or other at Raph. one last parting shot, then smooths his metaphorical ruffled feathers, clearing his throat.

“She was the leader of the pirates looking to purchase the mutagen,” Donnie says. Casey raises one eyebrow and glances up at Karai.

Snake mouths aren’t really meant for scowling, but Karai is somehow pulling the sullen look off anyway.

“And in the chaos of you being discovered,” Casey says, filling in all the gaps, “Karai got a dose of mutagen?”

Karai flashes her mouthful of sharp teeth, hissing balefully. She turns and dives into the ocean, black and white body vanishing into the depths. Leo winces and then sighs.

“Try not to talk about it too much,” Leo says, rubbing the back of his neck. “She’s only been a mutant for a few days and she’s still adjusting. We only just got her to calm down and listen about how _we_ didn’t drop that canister.”

“It was just the guy I punched,” Mikey says, shrugging. “He totally wiped out and then the canister went rolling all over the place and people kept _kicking it,_ which was majorly stupid, wow, and it ended up getting shattered right on Karai. Total accident, totally not our fault.”

A wave abruptly crashes down all them all, courtesy of the tail smacking against the surface of the water. Casey spits out seawater and curses, trying to sort out his now soaking hair, which is sticking _everywhere_ and making it feel impossible.

Raph wipes his face off, flicking the water away. “An accident, yes. Don’t mean she’s gonna forgive us for interrupting her black market shopping spree just yet.”

“At least she’s not trying to kill us anymore?” Leo says with a weakly light tone, to which his brother roll their eyes. Casey drags a strand of hair off his face and flicks it backwards, huffing with a grin.

Never a dull moment with the brothers. Casey can’t wait until April gets a load of _this_ new misadventure. It has teeth, a pissy attitude, and is apparently _pirate_ related, too.

Casey definitely wants in. But first.

“Okay, great talk everyone, fun sharing session,” Casey says, standing up, hands on his hips. “Now who wants the good broom and who wants the shitty broom? Because you’re definitely helping clean up the garbage you made me drop, plus since you just ruined my dad’s notebook.”

The brothers groan, but mumble agreements to the return of a favor. The water by the dockway swells with a long dark shape moving underneath it, not straying too far, but unwilling to surface right now. Casey takes the dripping notebook from Leo to set out to dry inside, and heads in to get the brooms as well. Practically whistling, despite the fact that he’s dripping wet.

**Notes for the Chapter:**

> dockway is slang for "dock walkway", since there aren't any sidewalks in Submerged.
> 
> and hello karai, nice of you to join the party. we'll know more about you at some point. and before anyone asks, no, leorai isn't going to be a thing. and besides them all eventually figuring out that karai is their half sister, karai is married to a certain second in command who's searching everywhere for her wife right now. its just fun to write socially awkward leo being happy about making friends with karai.
> 
> uhhhh sorry if this doesn't match the style of the other fics, its been a long while since i worked on this. ciao for another unknown amount of time!

**Author's Note:**

> leave comments and kudos below, [and don't forget to follow the blog!](https://submerged-tmnt.tumblr.com/)


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